Long chain N,N-dialkylhydroxylamines are effective in stabilizing polyolefin compositions against thermal degradation, as is seen in U.S. Pat. No. 4,590,231, particularly as processing stabilizers in the presence of phenolic antioxidants and/or other costabilizers.
N,N-Dialkylhydroxylamines have been discussed periodically in the prior art, and several reviews of the general methods of their preparation are available. These are notably S. Wawzonek et al, Organic Preparations and Procedures Int. 4(3), 135 (1972); and J. S. Roberts, Comprehensive Organic Chem., Ed. Sir D. Barton and W.D. Ollis, Chapter 6.4, p.185 (1979). Both of these reviews point out the facile Cope reaction involving the pyrolysis of an amine oxide to give an olefin and concomitantly a hydroxylamine.
Wawzonek et al describe the direct oxidation of secondary dialkylamines to the corresponding hydroxylamines using hydrogen peroxide, but point out the over-oxidation, low yields and other difficulties encountered.
British Patent No. 1,134,851 describes preparing N,N-dialkylhydroxylamines by oxidizing a tertiary amine with hydrogen peroxide to form the N-oxide in the presence of water, removing the water by azeotropic distillation and pyrolyzing the residue to form an olefin and the hydroxylamine.
A. C. Cope et al, Organic Reactions, Vol 11, Chapter 5, 317 (1960) describes the preparation of olefins from amines, the Hofmann elimination reaction and the pyrolysis of amine oxides. Emphasis is placed on the structure of the olefins prepared and N,N-di(lower alkyl)hydroxylamines are the hydroxylamines discussed.
U.S. Pat. No. 3,274,252 discloses the process for the aqueous oxidation of a tri(lower alkyl)amine with hydrogen peroxide in the presence of an alkali metal tungstate catalyst and alkali metal pyrophosphate to give the corresponding amine oxide followed by pyrolysis of the aqueous reaction mass to give the corresponding N,N-di(lower alkyl)hydroxylamine.
U.S. Pat. No. 3,709,942 discusses the preparation of N,N-dimethylhydroxylamine by the pyrolysis of aqueous alkyldimethylamine oxide.
U.S. Pat. No. 3,293,034 describes the preparation of various N,N-di(lower alkoxyalkyl)hydroxylamines by the oxidation of the corresponding secondary amine with hydrogen peroxide. Control of the reaction is difficult and the products are isolated by vacuum distillation in low yields.
U.S. Pat. Nos. 3,467,711 and 3,655,764 describe a process for preparing various N,N-di(lower alkoxyalkyl)hydroxylamines by the oxidation of the corresponding secondary amine with aqueous hydrogen peroxide in the presence of a metal sequestering agent such as ethylene diamine tetraacetic acid.
M.A.T. Rogers, J. Chem. Soc., 1955, 769 describes the preparation of N,N-dialkylhydroxylamines by a reverse Michael reaction on the N-oxides of the corresponding .beta.-dialkylaminopropionic esters or nitriles or selected Mannich bases under alkaline conditions. Said N-oxides are prepared by oxidation of the corresponding .beta.-dialkylamino compounds using monoperphthalic acid.
Rogers also describes the pyrolysis of tertiary amine oxides to give N,N-dialkylhydroxylamines.
Further Rogers points out that the direct oxidation of secondary amines by hydrogen peroxide is quite unsuitable which is not surprising in view of the strong reducing properties of hydroxylamines which are formed in the presence of hydrogen peroxide.
U.S. Pat. No. 3,243,462 describes the oxidation of lower dialkylamines to the corresponding lower dialkylhydroxylamines with hydrogen peroxide in the presence of a catalyst such as sodium tungstate or sodium vanadate. Only low yields of dialkylhydroxylamines are obtained.